The present invention relates to coating compositions, crosslinked coating compositions, coated substrates, and methods for producing the coating compositions and coated substrates. More particularly, the invention relates to coating compositions including polymeric particles and crosslinking agents comprising an organic compound having an isocyanate group or a blocked isocyanate group where the polymeric particles incorporate a monoalkenyl aromatic monomer, a vinyl-containing surfactant macromonomer, and at least one acrylic monomer having a hydroxyl, amine or carboxylic acid functional group.
Waterborne coatings are used to protect surfaces on numerous objects important to everyday life. For example, such coatings are commonly used to protect metals, wood, concrete, paper, and other important materials used in the construction of objects as diverse as homes, automobiles, bridges, retaining walls, and tin and aluminum cans.
Many surfaces such as metals are prone to oxidation, especially when exposed to salts, acids, bases, and other corrosive chemicals. Because waterborne coatings are used in a wide variety of applications and cover a wide variety of surface types, coatings that exhibit resistance to organic solvents, water, acids, salts, and other corrosive materials are highly desirable.
Although various waterborne coating compositions have been developed which show some degree of resistance to solvents and other chemicals, such coatings generally have a high cure temperature.
U.S. Pat. No. 4,814,514 and U.S. Pat. No. 4,939,283 issued to Yokota et al. disclose certain surface-active compounds which have a polymerizable allyl or methallyl group. The surface-active compounds are disclosed as being particularly useful as emulsifiers in the emulsion or suspension polymerization of various monomers such that aqueous suspensions of the polymer particles are produced.
U.S. Pat. No. 5,332,854 and U.S. Pat. No. 5,324,862 issued to Yokota et al. disclose anionic and nonionic vinyl-aromatic surfactants capable of reacting with other monomers, and thus being incorporated into polymers, during polymerization reactions.
Various vinyl aromatic surfactants referred to as Noigen RN, a nonionic surfactant, and Hitenol(trademark) BC, an anionic surfactant, are described in a technical bulletin published by DKS International, Inc. of Tokyo, Japan. Related polymerizable anionic surfactants referred to as Hitenol(trademark) A-10 are similarly described in another technical bulletin published by the same entity. Both publications disclose the preparation of polymers containing the surfactants.
U.S. Pat. No. 5,891,950 issued to Collins et al. disclose the preparation of water-based ink compositions containing a pigment and a polymer latex. The disclosed latex is either a non-carboxylic acid containing polymeric (polyamino) enamine latex or a mixture of a polymeric (polyamino) enamine latex and an acetoacetoxy-functional polymer latex. The polymeric (polyamino) enamine for use in the ink is disclosed as a reaction product of a surfactant-stabilized acetoacetoxy-functional polymer that may be prepared from a vinyl-containing anionic or nonionic reactive surfactant such as Hitenol(trademark) RN, Hitenol(trademark) HS-20, Hitenol(trademark) A-10, and Noigen RN.
U.S. Pat. Nos. 6,060,556 and 5,998,543 issued to Collins et al. disclose the composition, preparation, and end-use of waterborne compositions prepared from water-based latexes. The water-based latexes comprise dispersed, non-carboxylic acid containing waterborne polymeric amino-functional and acetoacetoxy-functional particles. The disclosed latex can be used in a variety of coating compositions such as paints, inks, sealants, and adhesives. Preparation of a surfactant-containing acetoacetoxy-functional polymer is disclosed which may be prepared using a vinyl-containing anionic or nonionic reactive surfactant such as Hitenol(trademark) RN, Hitenol(trademark) HS-20, Hitenol(trademark) A-10, and Noigen RN.
U.S. Pat. No. 6,028,155 issued to Collins et al. disclose the preparation and composition of surfactant-containing acetoacetoxy-functional polymers. The acetoacetoxy-functional polymers may be a surfactant-containing enamine-functional polymer, but is more preferably a surfactant-containing polymeric (polyamino) enamine. The disclosed non-carboxylic acid containing waterborne polymer compositions can be prepared with a high solids content while maintaining low viscosity, and the compositions are disclosed as useful in a variety of coating applications such as in paints, inks, sealants, and adhesives.
U.S. Pat. No. 5,539,073 issued to Taylor et al. discloses polymers useful in coating compositions. The polymers are prepared via free radical polymerization using ethylenically unsaturated monomers.
Various reactive anionic and nonionic surfactants are disclosed as suitable surfactants for use in the disclosed emulsion polymerization process.
U.S. Pat. No. 5,783,626 issued to Taylor et al. discloses allyl-functional polymers having pendant enamine moieties and preferably also possessing pendant methacrylate groups. The patent also discloses that amino-containing waterborne particles can be prepared by reacting propylene imine with carboxylic acid-containing latexes. Such amino-functionalized latexes were reacted with acetoacetoxyethyl methacrylate. Vinyl-containing anionic and ionic surfactants are disclosed as components which can be added to processes used for preparing the acetoacetoxy-containing polymers.
Although a number of references have disclosed polymerizable surfactants and polymers incorporating such surfactants, none of the references discloses a coating composition that comprises a crosslinking agent and a polymeric particle prepared from a vinyl-containing surfactant macromonomer that exhibits enhanced solvent resistance when crosslinked at low cure temperatures or such a coating composition which cures at faster line speeds at higher temperatures.
It would be highly desirable to have a coating composition that exhibits increased solvent resistance, chemical resistance, and hardness development at ambient cure temperatures.
The invention provides coating compositions that include polymeric particles, a crosslinking agent, and water. The polymeric particles include at least one incorporated monoalkenyl aromatic monomer, at least one incorporated vinyl-containing surfactant macromonomer, and at least one incorporated acrylic monomer. At least one incorporated acrylic monomer includes a hydroxyl functional group, or a carboxylic acid functional group. The crosslinking agent is an organic compound having at least one isocyanate group, at least one blocked isocyanate group, or at least one isocyanate group and at least one blocked isocyanate group. In one embodiment, coating compositions are provided in which the crosslinking agent is a polyisocyanate. In other coating compositions, the polymeric particles incorporate at least one acrylic monomer with a hydroxyl group and at least one acrylic monomer with a carboxylic acid functional group.
A method of preparing a coating composition includes mixing polymeric particles with a crosslinking agent to produce the coating composition. The polymeric particles include at least one incorporated monoalkenyl aromatic monomer, at least one incorporated vinyl-containing surfactant macromonomer, and at least one incorporated acrylic monomer.
At least one incorporated acrylic monomer of the polymeric particles includes a hydroxyl functional group, an amine functional group, or a carboxylic acid functional group. The crosslinking agent is an organic compound having at least one isocyanate group, at least one blocked isocyanate group, or at least one isocyanate group and one blocked isocyanate group. Preferred methods include a polyisocyanate crosslinking agent.
The invention also provides a method for preparing a coated substrate that includes coating a substrate with a coating composition according to the present invention.
The invention further provides coated substrates that include a substrate, preferably metal, coated with a coating composition according to the present invention. Coated substrates are also provided that include a substrate coated with a crosslinked coating composition according to the present invention.
Still further features and advantages of the invention will be apparent upon examination of the following detailed description.
A polymeric particle xe2x80x9csubstantially freexe2x80x9d of an item is a polymeric particle that contains less than 2%, more preferably less than 1%, and most preferably less than 0.25% (w/w) of the item.
A coating composition xe2x80x9csubstantially freexe2x80x9d of an item is a coating composition that contains less than 0.5% (w/w) of the item.
A polymeric particle that has a monomer xe2x80x9cincorporatedxe2x80x9d into it means that the monomer has reacted in a polymerization reaction and that the reacted monomer is chemically attached to the polymeric particle.
A coating composition with a polymeric particle incorporating a vinyl-containing surfactant macromonomer xe2x80x9cexhibits enhanced solvent resistancexe2x80x9d when the solvent resistance of the cured coating as judged by integrity and appearance after exposure to solvent is greater than that of a cured coating composition prepared under identical conditions except that the polymeric particle does not incorporate a vinyl-containing surfactant macromonomer, but rather where the coating composition includes the surfactant sodium dioctyl sulfosuccinate.
All ranges recited herein include all combinations and subcombinations included within that range""s limits. Therefore, a range from xe2x80x9c5-90%xe2x80x9d includes ranges from xe2x80x9c5-72%xe2x80x9d, xe2x80x9c12-65%xe2x80x9d, etc. A range of xe2x80x9cgreater than 100xc2x0 C.xe2x80x9d would include xe2x80x9cgreater than 112xc2x0 C.xe2x80x9d, xe2x80x9cgreater than 150xc2x0 C.xe2x80x9d, etc.
Generally, coating compositions according to the invention include a polymeric particle, a crosslinking agent, and water. Typically, the polymeric particles are prepared by an emulsion polymerization so that the polymeric particles are obtained as an aqueous dispersion. The polymeric particles of the coating composition include at least one incorporated monoalkenyl aromatic monomer, at least one incorporated vinyl-containing surfactant macromonomer, and at least one incorporated acrylic monomer. At least one incorporated acrylic monomer of the polymeric particle includes a hydroxyl functional group, an amine functional group, or a carboxylic acid functional group. The crosslinking agent is an organic compound having at least one isocyanate group, at least one blocked isocyanate group, or at least one isocyanate group and at least one blocked isocyanate group. Preferable crosslinking agents are polyisocyanates or compounds, polymeric or otherwise, with more than two isocyanate groups.
The polymeric particle for use in the method of the present invention incorporates at least one vinyl-containing surfactant macromonomer. The vinyl-containing surfactant macromonomer is preferably a vinyl aromatic surfactant macromonomer and more preferably is a vinyl aromatic anionic or nonionic surfactant macromonomer. Preferred vinyl-containing surfactant macromonomers for use in the present invention have the structure: 
where: R0 is an organic di-radical, R1 is H, a halogen, or a C1 to C22 linear or branched chain hydrocarbon group; R2 is H, a halogen, or a linear or branched chain C1 to C6 linear or branched chain hydrocarbon and the zigzag lines represent that the R2 group can be either cis or trans to the aromatic group; R3 is H, a halogen, or a C1 to C6 linear or branched chain hydrocarbon group; R4 is H or a C1 to C4 alkyl group; m is an integer ranging from 0 to 20; n is an integer ranging from 1 to 50; X is H, SO3xe2x88x92Y, P(xe2x95x90O)(OH)2, or a deprotonated form of P(xe2x95x90O)(OH)2; and Y is a cation such as sodium, lithium, potassium, ammonium, monoalkylammonium, dialkylammonium, trialkylammonium, or tetralkylammonium. More preferred vinyl-containing surfactant macromonomers for use in the present invention include those where m is 0 or 1; n is an integer from 5 to 25, more preferably 14 to 25; R2 is a methyl or H; R3 is H; R4 is H; and X is SO3xe2x88x92Y. In still more preferred vinyl-containing surfactant macromonomers n is 19, m is 0, and Y is an ammonium, a monoalkylammonium, a dialkylammonium, a trialkylammonium, or a tetraalkylammonium cation. In still other preferred vinyl-containing surfactant macromonomers, the vinyl-group of the vinyl-containing surfactant macromonomer is ortho to the alkoxy group bonded to the aromatic ring of the vinyl-containing surfactant macromonomer.
The polymeric particles in the coating compositions of the present invention incorporate at least one acrylic monomer and at least one monoalkenyl aromatic monomer in addition to incorporating at least one vinyl-containing surfactant macromonomer. At least one acrylic monomer incorporated in the polymeric particle preferably has a hydroxyl, amine, or carboxylic acid functional group. More preferred particles in the coating of the present invention incorporate at least one vinyl-containing surfactant macromonomer, at least two different acrylic monomers, and at least one monoalkenyl aromatic monomer. In especially preferred embodiments, the polymeric particles incorporate at least one acrylic monomer having a hydroxyl group such as, for example, hydroxyalkyl acrylates and hydroxyalkyl methacrylates.
Various acrylic monomers may be incorporated in the polymeric particle used in the present invention. Examples of acrylic monomers include, but are not limited to, acrylic acid, methacrylic acid, crotonic acid, esters of acrylic acid, esters of methacrylic acid, esters of crotonic acid, salts of acrylic acid, salts of methacrylic acid, and salts of crotonic acid. These are all examples of acrylic monomers including a carboxylic acid group.
Examples of acrylate and methacrylate monomers that may be incorporated in the polymeric particle include, but are not limited to, methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, i-butyl, t-butyl, n-amyl, i-amyl, n-hexyl, 2-ethylbutyl, 2-ethylhexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl, benzyl, phenyl, cinnamyl, 2-phenylethyl, allyl, methallyl, propargyl, crotyl, 2-hydroxyethyl, 2-hydroxypropyl, 2-hydroxybutyl, 6-hydroxyhexyl, 5,6-dihydroxyhexyl, 2-methoxybutyl, 3-methoxybutyl, 2-ethoxyethyl, 2-butoxyethyl, 2-phenoxyethyl, glycidyl, furfuryl, tetrahydrofurfuryl, tetrahydropyryl, N,N-dimethylaminoethyl, N,N-diethylaminoethyl, N-butylaminoethyl, 2-chloroethyl, 3-chloro-2-hydroxypropyl, trifluoroethyl, and hexafluoroisopropyl acrylates and methacrylates. More preferred acrylates and methacrylates include alkyl acrylates and methacrylates such as the various isomers of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, n-nonyl, and n-decyl acrylates and methacrylates. Other preferred acrylates and methacrylates include hydroxyalkyl acrylates and methacrylates such as, but not limited to 2-hydroxyethyl and 3-hydroxypropyl acrylate and methacrylate. Particularly preferred acrylic monomers for incorporation into the polymeric particles of the coating compositions according to the invention include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-ethylhexyl acrylate, and methacrylic acid.
Although, as described above, a large number of different acrylic monomers may be incorporated into the polymeric particles, a particularly useful combination of acrylic monomers for incorporation into a polymeric particle include 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, and methacrylic acid. These are especially preferred when combined with monomers such as styrene, xcex1-methylstyrene, or both. When used to prepare the polymeric particles, the following monomers are used in the following amounts where the ranges in parentheses respectively indicate the preferred range, the more preferred range, and the most preferred range of the monomer used by weight based on the total weight of the monomers: styrene (5-90%; 20-70%; 40-60%); methyl methacrylate (5-90%; 20-70%; 40-60%); 2-ethylhexyl acrylate (5-90%; 20-70%; 22-33%); ethyl acrylate (5-90%; 20-60%, 30-50%); hydroxyethyl acrylate (3-30%; 6-20%; 8-16%); hydroxyethyl methacrylate (3-30%; 6-20%; 8-16%); methacrylic acid (0-20%; 6-20%; 0-5%); vinyl-containing surfactant macromonomer (0-10%; 0.5-5%; 1-2%); octyl mercaptopropionate (0-5%; 0-1%; 0-0.1%); and butyl acrylate (5-90%; 20-70%; 25-45%). Polymer particles incorporating amine functional groups can be prepared by techniques known in the art for example such as those disclosed in the U.S. Pat. No. 5,998,543 issued to Collin and Taylor.
A variety of monoalkenyl aromatic monomers may be incorporated in the polymeric particle for use in the present invention. For example, suitable monoalkenyl aromatic monomers include, but are not limited to styrene, vinyltoluene, xcex1-methyl styrene, t-butyl styrene, vinylxylene, and vinylpyridine. More preferred monoalkenyl aromatic monomers include styrene and xcex1-methyl styrene. Although some of the vinyl-containing surfactant macromonomers incorporated in the polymeric particle are aromatic vinyl-containing surfactant macromonomers and could thus be classified as a type of monoalkenyl aromatic monomer, the term xe2x80x9cmonoalkenyl aromatic monomerxe2x80x9d as used herein is defined to not include the vinyl-containing surfactant macromonomers.
A variety of other monomers may be incorporated in the polymeric particle for use in the present invention. One such monomer that may be incorporated in the polymer includes vinyl ester monomers. Preferred vinyl esters include, but are not limited to, those having the structure H2Cxe2x95x90C(R5)xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94R6 where R5 is either H or an alkyl group having from 1 to 5 carbon atoms and R6 is an alkyl group having from 1 to 22 carbon atoms. In a more preferred embodiment, at least one of the carbon atoms of the R6 alkyl group is bonded to at least three other carbon atoms. Thus, more preferred vinyl ester monomers include those with a tertiary or quaternary carbon in the R6 alkyl group. Examples of a few of these more preferred vinyl ester monomers include, but are not limited to: H2Cxe2x95x90C(R5)xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94C(CH3)3, H2Cxe2x95x90C(R5)xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CH2xe2x80x94(CH3)3, H2Cxe2x95x90C(R5)xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CH(CH3)xe2x80x94CH2xe2x80x94CH3, H2Cxe2x95x90C(R5)xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CH2xe2x80x94C(CH3)2CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH3, and H2Cxe2x95x90C(R5)xe2x80x94C(xe2x95x90O)xe2x80x94C(CH3)2xe2x80x94CH2xe2x80x94CH3.
It is not necessary or required that the polymeric particle for use in the coating compositions contain metal chelating groups such as acetoacetoxy, amine, or enamine groups. Rather, it has been found that metal surfaces coated with coating compositions including a crosslinking agent and polymeric particles that do not contain these groups exhibit enhanced resistance to organic solvents even when cured at ambient temperature. However, these groups may be present if so desired. The fact that these groups can be excluded from the polymeric particles for use in the present invention helps to reduce the costs associated with using monomers such as acetoacetoxyethyl methacrylate. Furthermore, because the polymeric particles do not require any polymeric amine or enamine, acid-functional acrylic monomers such as, but not limited to, acrylic acid, methacrylic acid, and crotonic acid may be incorporated without any resulting cloudiness or flocculation. The polymeric particle need also not contain trimethylolpropane triacrylate as coating compositions containing polymers prepared without this material have shown excellent solvent resistance on surfaces.
The coating compositions of the present invention include a crosslinking agent. The crosslinking agent(s) is an organic compound having at least one isocyanate group, at least one blocked isocyanate group, or at least one isocyanate group and at least one blocked isocyanate group. Preferred crosslinking agents of the present invention are polyisocyanates meaning that they have two or more isocyanate groups per molecule. Preferred crosslinking agents include polyisocyanates with two, three, four, or more isocyanate groups per molecule. Crosslinking agents of the invention may be polymeric compounds or small molecules.
The phrase xe2x80x9cblocked isocyanate groupxe2x80x9d refers to a functional group that breaks down to form an isocyanate group and a blocking compound. Any blocked isocyanate group known to those skilled in the art may be employed in the present invention. Examples of blocking compounds that may be used to prepare blocked isocyanates include, but are not limited to, phenols; alcohols; oximes such as, but not limited to, those prepared from methyl ethyl ketone, acetone, and diisopropyl ketone; xcex5-caprolactam, and diethyl malonate. Upon heating, blocked isocyanate groups are unblocked to produce reactive isocyanate groups that will react with hydroxyl functionalities on the polymeric particles to produce polyurethane crosslinked coatings that exhibit enhanced resistance to water, organic solvents, acid solutions, and other chemicals. Particularly preferred crosslinking agents include unblocked isocyanates such as Bayhydur(copyright) XP 7063 (Bayer, Germany) and Tolonate(copyright) WT 2102 brand of polyisocyanate available from Rhodia (Cranbury, N.J.), and blocked isocyantates such as Bayhydur(copyright) BL 116 brand of polyisocyanate available from Bayer (Germany) and Tolonate(copyright) WT 1000 brand of polyisocyanate available from Rhodia (Cranbury, N.J.).
One group of preferred isocyanates includes hydrophilic isocyanates such as, but not limited to, trimers of simpler isocyanates or polyisocyanates with one or more isocyanate group reacted with a surfactant to improve incorporation and hydrophilic character. Other preferred isocyanates include hydrophobic isocyanates that are emulsified to improve incorporation.
Polymeric particles containing carboxylic acid functional groups will also react with the crosslinking agent so the polymeric particles may incorporate an acrylic monomer containing this functionality in place of or in addition to the acrylic monomers with the hydroxyl functional group. However, polymeric particles incorporating acrylic monomers with hydroxyl functional groups or incorporating at least one acrylic monomer with a hydroxyl functional group and at least one acrylic monomer with a carboxylic acid functional group are especially preferred.
The polymeric particle for use in the present invention may be prepared using any method known to those skilled in the art for incorporating radically-polymerizable ethylenically-unsaturated monomers into a polymer. The polymer may be prepared by continuous, semi-batch or batch processes using any type of reactor known to those skilled in the art. Various polymerization processes are disclosed in U.S. Pat. No. 4,414,370, U.S. Pat. No. 4,529,787, and U.S. Pat. No. 4,546,160 and these patents are herein expressly incorporated by reference in their entirety.
The polymeric particle may also be prepared by emulsion polymerization techniques and methods known to those skilled in the art. For example, a suitable latex containing incorporated vinyl-containing surfactant macromonomer may be prepared by adding a standard initiator such as, but not limited to, ammonium persulfate to an aqueous heated solution of a vinyl-containing surfactant macromonomer such as Hitenol(trademark) BC-20 available from DKS International, Inc. (Tokyo, Japan) while it is stirred in a resin kettle. A monomer feed containing additional monomers may then be added to the resulting mixture. For example, an emulsion feed containing more of the vinyl-containing surfactant macromonomer; acrylic monomers such as a mixture of methacrylic acid, 2-hydroxyethyl acrylate and 2-ethylhexyl acrylate; and an monoalkenyl aromatic monomer such as styrene or a mixture of monoalkenyl aromatic monomers, may be added to the solution.
The monomer feed may contain additional components such as, but not limited to, solvents and chain transfer agents. For example, any conventional chain transfer agent such as octyl mercaptopropionate may be present in the monomer feed. Once monomer addition is complete, oxidants such as ferrous sulfate may be added to the mixture followed by addition of initiators such as t-butyl hydroperoxide dissolved in aqueous solution containing isoascorbic acid and ammonium hydroxide. The pH of the aqueous product is generally increased to value of greater than about 8 by addition of ammonium hydroxide solution. Preferred coating compositions prepared from aqueous dispersion containing the polymeric particles generally have a pH of greater than 7 and less than about 10. More preferably, the pH of the coating composition is greater than 8 or about 8.
The coating compositions may be prepared by mixing polymeric particles according to the invention with a crosslinking agent according to the invention. Curing agents may also be added to the coating compositions. The ratio of polymeric particles to crosslinking agent by weight preferably ranges from about 95:5 to about 65:35, more preferably ranges from about 92:8 to about 70:30, still more preferably from about 90:10 to about 80:20. In one embodiment, coating compositions are obtained using a ratio of polymeric particles to polyisocyanate-based crosslinking agent of about 80:20 and about 90:10 by weight. Generally, the ratio of isocyanate groups in the crosslinking agent to hydroxyl groups in the polymeric particle will range from 1:1 to 2:1 or more preferably will be about 1.5:1.
Because the rate at which unblocked isocyanate crosslinking agents unblock to produce reactive isocyanate varies depending on the reactivity and steric factors associated with the blocking group and the isocyanate group, curing temperatures should be adjusted based upon the particular type of isocyanate groups (e.g. aliphatic or aromatic) and blocking group.
Preferably, polymeric particles are mixed with the crosslinking agent at about room temperature or a temperature ranging from about 21xc2x0 C. to about 25xc2x0 C. when using unblocked isocyanates. The temperatures will vary depending on the particular blocking agent used when blocked isocyanates are utilized. Generally, the isocyanate(s) is cut to the desired percent of solids by dilution with a solvent which mixture is then added under agitation to the polymeric particles.
Mixing of the polymeric particles with the crosslinking agent and optionally, but preferably, additional components may be accomplished using any well known agitation method known to those skilled in the art. Thus, the mixing may be accomplished with a blender or any other high speed mixing device. Generally, introduction of the crosslinking agent involves preblending the crosslinking agent with a water miscible solvent that may include water. The blend containing the crosslinking agent is typically added to the polymer particles while agitated using any high speed mixing apparatus as described above. Blade speeds of 50 revolutions per minute or higher are generally preferred. Pigments such as TiO2 may be used to produce white compositions. Similarly, other pigments or combinations of pigments known to those skilled in the art may be added to produce a desired color for the formulation. Furthermore, pigments may be excluded from the formulations of the present invention to produce colorless transparent coatings.
A coated substrate may be prepared by coating a substrate with a coating composition according to the present invention. The coating may then be allowed to dry at room temperature or may be dried at elevated temperature. A coated substrate having a crosslinked coating composition is typically prepared by heating (curing) the coated substrate to a temperature of greater than about 90xc2x0 C., preferably at a temperature between 90xc2x0 C. and 180xc2x0 C., and also preferably to a temperature of greater than about 180xc2x0 C. As noted above, however, the curing temperature should be varied to suit the crosslinking agent included in the formulation. It has been discovered that the temperature plays an important role in determining the solvent and chemical resistance of a coating on a substrate. Additionally, curing catalysts may be added to lower the curing temperature while still obtaining the same solvent resistance afforded at higher cure temperatures. Additionally, any suitable alternative method of curing well known in the art, such as ultraviolet light, may be utilized in addition to or in place of thermal curing.
Various substrates may be coated with the coating compositions of the invention. A preferred coated substrate is a metal such as, but not limited to, aluminum, copper, tin, steel, or iron coated with a coating composition according to the present invention. Other substrates that may be coated include plastic and paper surfaces. Particularly preferred coated substrates are coated aluminum and steel. The substrate can take various forms.
The coating composition may be applied to a metal or any other surface using any technique known to those skilled in the art. Thus, the polymeric particle may be applied to a metal surface as a clear coat formulation. Alternatively, the polymeric particle may be applied as one of several components in a paint. Such paints can be readily prepared by mixing a latex prepared as described above with a number of ingredients using conventional techniques. For example, the latex may be mixed with water, a conventional pigment such as, but not limited to, TiPure(trademark) R-706 TiO2 pigment or TiPure(trademark) R-900 TiO2 pigment, both available from E.I. DuPont de Nemours (Wilmington, Del.) and various conventional additives such as, but not limited to, organic solvents, defoamers, conventional surfactants, associative thickeners, plasticizers, flash rust inhibitors, and dispersants. Non-limiting representative examples of some of these components are CT-324 dispersant available from Air Products (Allentown, Pa.); Surfynol(copyright) CT-151 dispersant available from Rohm and Haas Company (Philadelphia, Pa.); Surfynol(copyright) 104DPM conventional surfactant available from Rohm and Haas Company (Philadelphia, Pa.); BYK 020 defoamer available from BYK Chemie (Wallingford, Conn.); Dehydran(copyright) 1620 defoamer available from Henkel Corp. (Ambler, Pa.); (copyright)PUR 40 an associative thickener available from King Industries, Inc. (Norwalk, Conn.); DSX(copyright)-1550 associative thickener available from Henkel Corp. (Ambler, Pa.); RM-825(trademark) associative thickener available from Rohm and Haas Company (Philadelphia, Pa.); KP-140(copyright) tributoxy ethyl phosphate available from FMC Corp. (Philadelphia, Pa.); and Raybo(trademark) 60 flash rust inhibitor available from Raybo Chemical Company (Huntington, W.Va.). In addition, one skilled in the art will recognize that other types of polymeric particles may be included in the coating compositions of the present invention. For example, polymeric particles that do not incorporate acrylic monomers with hydroxyl functional groups, amine functional groups, or carboxylic acid functional groups may be mixed with polymeric particles that do incorporate such acrylic monomers to produce coating compositions that include two or more types of polymeric particles.
Surprisingly and unexpectedly, it has been found that coating compositions comprising a polymeric particle incorporating vinyl-containing surfactant macromonomer(s) and a crosslinking agent show drastically improved solvent resistance and resistance to aqueous acid solutions compared to similar coating compositions that contain polymers without incorporated vinyl-containing surfactant macromonomers, but rather contain conventional surfactants. It has been found that the solvent resistance for the coating compositions that contain crosslinking agents such as the preferred crosslinking agents of the invention may be better than those with a conventional surfactant, but without the incorporated vinyl-containing macromonomer, even when the cure temperature of the coating is lower for the compositions prepared from the vinyl-containing surfactant macromonomer.
The coating compositions may be applied to a substrate using any technique known to those skilled in the art including, but not limited to, spray coating, brush coating, powder coating, and application with applicator blades.
The coating compositions applied to substrates are generally in an aqueous polymeric dispersion such as, but not limited to, a latex.
However, the polymeric particles and crosslinking agents may also be dissolved in an organic solvent and thus applied to the surface. Thus, the coating composition of the invention may be painted on a substrate surface using any of various techniques known to those skilled in the art. Additionally, the coating composition may be applied in other forms including, but not limited to, as a powder coating. A solution containing the polymeric particles for application to the substrate may contain various other ingredients as described above and demonstrated below.
The coating compositions of the present invention may be formulated as clear coats, as paints, as inks, as coating for textiles, and as coatings for wood.
The invention is further described in the following non-limiting examples.